As an elastic fluorocopolymer (hereinafter sometimes referred to as fluororubber), a vinylidene fluoride/hexafluoropropylene copolymer, a tetrafluoroethylene/propylene copolymer, a tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer, etc., are known.
These elastic fluorocopolymers are excellent in heat resistance, oil resistance, chemical resistance, etc., and can be employed in a severe environment which general materials cannot resist. However, these elastic fluorocopolymers are poor in the reactivity and are insufficient in the crosslinkability and the adhesion to another material, and heretofore, a method for enhancing the reactivity by introducing a reactive functional group has been proposed (e.g. JP-A-11-116634).
Generally speaking, a rubber material, except for some thermoplastic elastomers, is required to develop suitable physical properties by the crosslinking reaction. Therefore, even in a molecule of an elastic fluorocopolymer, a crosslinkable functional group is introduced. In a vinylidene fluoride/hexafluoropropylene copolymer, as a reactive functional group, an iodine atom (e.g. Masayoshi Tatemoto, Japanese Journal of Polymer Science and Technology, 49(10), 765 to 783 (1992)) or an unsaturated bond (e.g. JP-B-62-56887) has been proposed.
A tetrafluoroethylene/propylene copolymer is superior to the vinylidene fluoride/hexafluoropropylene copolymer in view of chemical resistance, especially amine resistance and high-temperature steam resistance (e.g. JP-A-6-306242). With regard to such a copolymer, a method of copolymerizing a monomer containing a crosslinkable functional group such as CF2═CFOCF═CFCF3, CF2═CFOCF2CF(CF3)OCF═CFCF3 or CF2═CFCF2CF═CFCF3 (e.g. JP-B-62-56887), has been proposed, but the effect thereof was insufficient.
Further, with respect to a tetrafluoroethylene/propylene/vinylidene fluoride copolymer, there has been a problem such that if a polyol crosslinking agent is used, when a vinylidene fluoride/hexafluoropropylene copolymer is mixed or an acidic filler such as silica is used with such a copolymer, a crosslinking inhibition is likely to take place.
Accordingly, it is desired to develop a crosslinkable elastic fluorocopolymer containing no iodine atom, and having crosslinkable functional groups introduced to its molecules, without taking any cumbersome steps. Further, it is desired to develop a composition containing such an elastic fluorocopolymer, which is excellent in the crosslinkability.